A charge trapping semiconductor memory typically has an array of charge trapping memory cells arranged in columns and rows, where each one of the memory cells is structured as a transistor including a gate dielectric that typically consists of a charge trapping storage layer sandwiched in between two boundary layers. In general, storage layer materials have a smaller energy band gap and a larger trap density than boundary layer materials so that charge carriers trapped in the storage layer remain localized. Typically, nitrides are used as storage layer materials, while oxides are used as boundary layer materials. Depending on the actual configuration, charge carriers can be transferred from the channel region to the storage layer using channel hot electrons (CHE) or Fowler-Nordheim tunneling. Erasing a charge trapping memory cell may be effected by injecting hot holes or by Fowler-Nordheim tunneling.
In a typical common source memory cell architecture, conductive source lines connect source regions of a column and conductive word lines that are arranged in parallel alignment to the source lines connect gate electrodes of a column and are used to select a single memory cell. Conductive bit lines are arranged above the word and source lines orthogonally aligned therewith and are in electric contact with drain regions. Different therefrom, in a typical virtual ground architecture, bit lines are in electric contact with both source and drain regions, where every two adjacent bit lines are used for programming and sensing of a memory cell.
Document DE 10258194 A1 describes a semiconductor memory having charge trapping memory cells in virtual ground architecture, where directions of current flows through the channel regions are aligned vertically to word lines and bit lines are arranged above the word lines isolated therefrom. Local interconnects (jumper connections) are provided between the word lines isolated therefrom that are connected to the bit lines. With regard to a consecutive numbering of the storage transistors, these local interconnects on one side of a word line, respectively, electrically conductively connect a source/drain region of an even-numbered storage transistor with a source/drain region of a consecutive odd-numbered storage transistor, and, on the opposing side of that word line, these local interconnects respectively electrically conductively connect a source/drain region of an odd-numbered storage transistor with a source/drain region of a consecutive even-numbered storage transistor. Also, word lines can be contacted with word line straps to reduce resistivity thereof.
Charge trapping memory cells of above document DE 10258194 A1 are structured in planar configuration, in which, however, severe problems as to a further down-scale of the memory cells can arise. More particularly, scaling down the memory cells results in shorter and shorter lengths of channel regions that is to say distance of the regions in between source/drain regions, rendering a punch-through of the memory cells more likely. Otherwise, usage of the memory cells in a multi-bit storage mode essentially requiring localized charge distributions on drain-sides and source-sides of the storage layers of the memory cells may result in a detrimental overlap of charge distributions disabling a clear discrimination of logic states.